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Segment Information (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2019 USD ($) business_segments | Sep. 30, 2018 USD ($) | Sep. 30, 2017
Segment Reporting [Abstract] |  |  |
Number of Reportable Segments | business_segments | 2 |  |
Revenue, Major Customer [Line Items] |  |  |
Receivables, net | $ 172.8 | $ 164.3 |
Intangible Assets, Net (Including Goodwill) | 529.4 | 420.2 |
Total assets | $ 1,337.3 | 1,291.9 |
Document Period End Date | Sep. 30, 2019 |  |
Mueller Co. [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
Intangible Assets, Net (Including Goodwill) | $ 508.2 | 396.9 |
Total assets | 1,107.8 | 843.9 |
Mueller Technologies [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
Intangible Assets, Net (Including Goodwill) | 21.2 | 23.3 |
Total assets | $ 100.3 | $ 87.1 |
Customer Concentration Risk [Member] | Major Customers, Group One | Sales Revenue, Goods, Gross [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 53.00% | 54.00% | 53.00%
Customer Concentration Risk [Member] | Major Customers, Group Two | Sales Revenue, Goods, Gross [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 34.00% | 34.00% | 34.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 18.00% | 19.00% | 18.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member] | Mueller Co. [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 17.00% | 18.00% | 17.00%
Customer Concentration Risk [Member] | Ferguson Enterprises | Sales Revenue, Goods, Gross [Member] | Mueller Technologies [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 30.00% | 28.00% | 24.00%
Customer Concentration Risk [Member] | HDS IP Holdings, LLC [Member] | Sales Revenue, Goods, Gross [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 16.00% | 15.00% | 16.00%
Customer Concentration Risk [Member] | HDS IP Holdings, LLC [Member] | Sales Revenue, Goods, Gross [Member] | Mueller Co. [Member] |  |  |
Revenue, Major Customer [Line Items] |  |  |
10 largest customers | 18.00% | 17.00% | 17.00%

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